Increasing the total yield of distillates and gasoline obtained from crude petroleum has long been an important refining problem, especially in areas where only limited cracking capacity is available. Increasing the yield of distillates by increasing the distillate end point is often restricted by unacceptable high pour/cloud points of the resulting fuels.
In typical refinery operations, products include, from lighter to heavier products, LP gas, solvents, motor gasoline, jet fuel, kerosene, diesel fuel, distillate burner fuels, residual fuel oil, lube oil, and waxes (microcrystalline and paraffin). Of particular interest are those liquid hydrocarbons boiling in the 400.degree.-850.degree. F. range. These include jet fuel, kerosene, diesel fuel, distillate burner fuel, and residual fuel oil. The end points of these hydrocarbon fractions are limited to meet specification pour points and cloud points. For example, normally in a topping-reforming operation, the about 650.degree. F.+ residium is rejected as diesel to distillate burner fuels and the like. Often there is a high economic incentive for refiners to increase jet fuel, kerosene and diesel fuel yield and decrease lower burner fuels output per barrel of crude. To achieve this objective, it is highly desirable to convert as much of the 650.degree. F. fraction of the residium into lower pour/cloud point diesel fuel.
One method of reducing the pour/cloud points is to blend lighter cuts material, such as kerosene, with the diesel fuel. However, such a method is not cost effective since the lighter material can be sold for higher prices. For example, kerosene can be sold as jet fuel.
Another method to achieve the above is to utilize catalytic dewaxing. Catalytic dewaxing of petroleum and synthetic crude oil fractions in the presence of shape selective catalysts capable of selectively cracking n-paraffins and isoparaffins is well known. For example, U.S. Re. Pat. No. 28,398 (Chen et al), which is a reissue of U.S. Pat. No. 3,700,585, discloses the use of shape selective crystalline aluminosilicate zeolite ZSM-5 in catalytic dewaxing processes directed at removing high freezing point paraffins from jet fuel to lower the freezing point, improve the octane rating of naphtha fractions and lower the pour point of lube oil base stocks. According to Chen et al, the shape selective cracking ability of crystalline aluminosilicate ZSM-5 permits selective cracking of n-paraffins and certain isoparaffins without substantial cracking of desirable feed components such that improved catalytic dewaxing products are obtained under both hydrotreating and hydrocracking conditions. Chen et al also discloses the use of crystalline aluminosilicate zeolite ZSM-5 associated with hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium, such metals being associated with the zeolite by exchange or impregnation.
European Patent Application No. 0079778 discloses a process for catalytic dewaxing-hydrotreating of hydrocarbon feed materials comprising contacting the feed with hydrogen under catalytic dewaxing-hydrotreating conditions in the presence of a catalyst comprising a shape selective zeolitic cracking component and a hydrogenating component of improved thermal stability comprising a chromium component, at least one other Group VIB metal component and at least one Group VIII metal component. According to a specific aspect of the invention, the catalytic dewaxing-hydrotreating process is employed to convert hydrocarbon feeds of either high or low quality to lube oil base stocks of high viscosity index, low pour point and good stability in a single step.
U.S. Re. Pat. No. 30,529 (Reynolds), which is a reissue of U.S. Pat. No. 4,100,056, discloses catalytic dewaxing of atmospheric and vacuum distillates in the presence of a catalyst containing mordenite in hydrogen form and a Group VI or Group VIII metal to obtain naphthenic lube oils of intermediate viscosity index and pour points ranging from -46.degree. to -7.degree. C. (-50.degree. to 20.degree. F.).
U.S. Pat. No. 4,222,855 to Pelrine et al discloses catalytic dewaxing of 232.degree.-566.degree. C. (450.degree.-1,050.degree. F.) hydrocarbon fractions to produce high viscosity index lube oils employing a catalyst containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35, preferably in hydrogen form and associated with platinum, palladium, or zinc. According to Pelrine et al, the use of catalysts containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35 gives products of higher viscosity index and lower pour point than products obtained through the use of crystalline aluminosilicate zeolite ZSM-5.
U.S. Pat. No. 4,247,388 (Banta et al) is directed to improving crystalline aluminosilicate zeolites such as ZSM-5 in terms of dewaxing performance by treatment to adjust alpha activity. The alpha activity is adjusted by partial replacement of cationic sites of the crystalline aluminosilicate zeolite with basic cations such as sodium, by partial coking of the zeolite, by employing the zeolite in combination with an inert matrix material, by manipulating the silica to alumina ratio of the zeolite to provide a relatively high ratio, or preferably, by steaming. Crystalline aluminosilicate zeolites adjusted in terms of alpha activity can be employed in association with exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium.
U.S. Pats. Nos. 4,251,348 and 4,282,085 (both O'Rear) are directed to processes similar to those described hereinabove wherein a low nitrogen content petroleum distillate fraction boiling from 82.degree.-649.degree. C. (180.degree.-1,200.degree. F.) is contacted with crystalline aluminosilicate zeolite in a form substantially lacking in hydrogenation activity to form an effluent which then is fractionated into an upgraded product stream and a C.sub.3 -C.sub.4 olefin fraction. If desired, the crystalline aluminosilicate zeolite can be dispersed in a porous matrix having only insubstantial cracking activity. Suitable matrix materials include pumice, firebrick, diatomaceous earth, alumina, silica, zirconia, titania, amorphous silica-alumina mixtures, bentonite, kaolin, silica-magnesia, silica-zirconia or silica-titania.
U.S. Pat. No. 4,259,174 (Chen et al) discloses catalytic dewaxing of hydrocarbon feeds to reduce pour point and produce high viscosity index distillate lube oil stocks in the presence of a synthetic offretite crystalline aluminosilicate zeolite catalyst which may contain exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium. The crystalline aluminosilicate zeolite may be dispersed within a matrix of alumina, silica, silica-alumina, etc.
An abstract of British patent No. 2,005,120 (Mobil) discloses a method for reclaiming or upgrading contaminated, dewaxed lube oil base stocks having a tendency to form a waxy haze during storage, comprising contacting the oil with hydrogen at 260.degree.-357.degree. C. (550.degree. -674.degree. F.) and space velocity of 2-10 in the presence of a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least 12 and a constraint index of 1-12.
The majority of the above line of references utilize one form or the other of crystalline aluminosilicate zeolite catalyst. Crystalline aluminosilicates are expensive and not readily available. Furthermore, aluminosilicates are known to be sensitive to steam and contaminants such as nitrogen and sulfur.
In most petroleum processing operations, it is conventional to pretreat the charge stock in some manner calculated to remove sulfur, metals and/or nitrogen from the charge stock prior to converting and upgrading such charge stock. Thus, catalytic hydrodesulfurization is commonly used in refineries. It normally precedes reforming and other conversion processes because sulfur, metals and nitrogen present in the charge stock often have detrimental effects on hydrocarbon conversion catalysts. Such contaminants tend to concentrate in the heavier petroleum fractions and thus would be present in the middle range fractions of kerosene and diesel fuel. Thus, it is common to subject these fractions to hydrodesulfurization and dewaxing.
Several patents discuss the relationship between hydrodesulfurization (often referred to as heavy distillate hydrotreating) and dewaxing. For example, U.S. Pat. No. 3,894,938 to Gorring et al discloses a process for catalytic dewaxing and desulfurization of high pour point, high sulfur gas oils to lower their pour point to about 10.degree. F. or lower and their sulfur content by contacting a high pour point gas oil first with a ZSM-5 type zeolite hydrodewaxing catalyst which may contain a hydrogenation/dehydrogenation component, in the presence or absence of added hydrogen under low pressure conditions, followed by conventional hydrodesulfurization processing of the dewaxed intermediate. Gorring states that the sequence of first dewaxing with a ZSM-5 catalyst and subsequent hydrodesulfurization (HDS) results in liquid yield levels of about 84% and dewaxing catalyst life of about 20-400 days between regenerations. Gorring further states that reversing the sequence of operations, i.e., HDS followed by dewaxing, drastically reduced the ZSM-5 catalyst life to about 1-24 hours between regenerations.
U.S. Pat. No. 4,394,249 to Shen discloses a process wherein a hydrocarbon feedstock is desulfurized in a conventional hydrodesulfurization process unit (HDS) and then conducted into a catalytic dewaxing process unit (CDW). The cascading relationship of the HDS/CDW units enables the operator of the plant to recover a substantial portion of thermal energy from a number of process streams and decreases the size of the compressor required in the plant. The patent teaches a very specific sequence and mechanical systems to recover thermal energy from the various process streams and transfer such from one unit operation to another. The CDW catalyst proposed is an aluminosilicate. No mention is made of catalyst life or liquid yield.
U.S. Pat. No. 4,400,265 to Shen discloses a process wherein a high pour point, high sulfur content gas oil is processed in a combination process wherein the gas oil is first catalytically dewaxed and then hydrodesulfurized in a cascade system which enables the two operations to be integrated through a common hydrogen system and whereby substantial quantities of thermal energy are recovered for reuse resulting in significant energy conservation. Again, this patent is directed to the mechanics of the operation and not the chemistry such as CDW catalyst life and liquid yields.
U.S. Pat. No. 4,428,825 (Ward et al) discloses a process for the production of lubricating oils which involves hydrodewaxing over a composite catalyst having a Group VIB or Group VIII metal component on an aluminosilicate or silicalite support in the presence of added ammonia or ammonia precursors. The patentees suggest that suitable feedstocks contain organosulfur and/or organonitrogen compounds to provide total sulfur and total nitrogen contents within the range of 50-1000 ppm and 50-400 ppm, respectively. Preferably, the catalyst is sulfided and such sulfiding may be accomplished by placing the catalyst in service in the oxide form such that it is contacted with organosulfur compounds in the feedstock. The Ward procedure is said to consume less hydrogen and provide a product of increased viscosity index.
U.S. Pat. No. 4,309,275 to Mulaskey discloses a catalytic dewaxing process in which a paraffinic hydrocarbon containing feedstock, ranging from napthta up through lube oil stocks but preferably boiling in excess of 200.degree. C., is contacted with a silicalite catalyst to produce an effleunt of greater olefin content than the feed. Mulaskey discloses that if sulfur compounds are present in the feed it can be lightly hydrotreated to less than 100, and preferably less than 50, ppm in order to lessen the possibility of mercaptan producing reactions. Feedstocks disclosed in Mulaskey include vacuum gas oils and neutral lube oil stocks containing about 2 wt. % and 6 ppm sulfur, respectively, and having initial boiling points in excess of 300.degree. C.
U.S. Pat. No. 4,439,329 to Eberly et al discloses a hydroprocessing process involving simultaneous hydrodesulfurization and pour point reduction of sulfur contaminated feed streams over a catalyst comprising silicalite composited with a nonzeolitic inorganic oxide support having a hydrogenation component associated therewith. Feedstocks containing from about 0.3-5 wt. % sulfur are disclosed as being treated over silicalite catalyst modified by the inclusion of about 6-12% cobalt and molybdenum oxides.